Sensor with constant airgap

ABSTRACT

An electrical sensor for sensing rotational speed between a pair of relatively rotatable members with the sensor including a pair of relatively rotatable poles being mounted, such that there will be substantially no change in airgap despite relative radial and axial movement between the relatively rotatable members.

United States Patent Watt et al.

[ 51 Mar. 14, 1972 [54] SENSOR WITH CONSTANT AIRGAP [72] Inventors: JohnA. Watt, Ann Arbor, Mich.; Hugh E.

Riordan, Wycoff, N .J [73] Assignee: Kelsey-Hayes Company, Romulus,Mich. [22] Filed: June 15, 1970 [21] Appl. No.: 48,868

Related U.S. Application Data [63] Continuation of Ser. No. 741,735,July 1, 1968, abandoned.

[52] U.S. Cl. ..3l0/67 R, 310/75 R, 310/156, 310/168, 310/268 [51] Int.Cl. ..II02lt 7/18 [58] Field of Search ..310/268, 261-269, 310/154-156,67, 67.1, 74, 75, 103, 106, 109, 209,

[56] References Cited UNITED STATES PATENTS 2,658,157 11/1953 Brouwer..3l0/156 2,499,036 2/ 1950 P1antet..... .310/103 X 2,956,187 10/1960Wood ..3l0/75 IBM Technical Disclosure Bulletin, W. R. Gafford,Self-Aligning Bearing, Vol. 1 1, No. 3, 8/68.

Primary Examiner-.1. D. Miller Assistant Examiner-B. A. ReynoldsAttorney-Hamess, Dickey & Pierce [57] ABSTRACT An electrical sensor forsensing rotational speed between a pair of relatively rotatable memberswith the sensor including a pair of relatively rotatable poles beingmounted, such that there will be substantially no change in airgapdespite relative radial and axial movement between the relativelyrotatable members.

11 Claims, 5 Drawing Figures SENSOR WITH CONSTANT AIRGAP This is acontinuation of application Ser. No. 741,735, filed on July 1, I968, nowabandoned.

SUMMARY BACKGROUND OF THE INVENTION The present invention relates toelectrical speed sensors.

In sensing the rotational speed at the rear wheels of a vehicle, adesirable location for the sensor is between the axle shaft flange andaxle housing of the rear wheel. However, it has been found that undersevere load conditions the rear axle shaft undergoes substantial radialdeflection relative to the housing. With a sensor construction having apair of relatively rotatable pole members, one being fixed to the axlehousing and the other being fixed to rotate with the axle shaft, it hasbeen found that the extreme radial and/or axial deflections under severeload of the axle shaft cause substantial variation in the airgap betweenthe sensor pole members and in some cases could cause the two members toengage resulting in damage to the sensor. The problem of engagement canbe avoided by providing a sufficiently large airgap or spacing betweenthe two sensor pole members such that even under the most extreme loadconditions of the axle shaft such engagement would not occur. However,with such a construction a relatively wide airgap would be requiredreducing the efficiency of the sensor. In the present invention theairgap is maintained at a minimum and the sensor pole member secured tothe axle shaft is mounted in a construction such that the pole membermounted to axle shaft will not be moved axially or radially despiterelative movement of the axle shaft hence permitting the provision of adesired minimum airgap. Hence a highly efficient construction can beprovided.

Therefore, it is an object of the present invention to provide animproved sensor construction for sensing relative rotation between tworelatively rotating members.

It is another object of the present invention to provide a new andimproved sensor construction of the above-described type in which thesensing rings or poles are secured such that a substantially constantairgap is maintained despite extreme load conditions causing relativeradial and/or axial motion between the members whose relative rotationalspeed is being sensed.

It is another object of the present invention to provide a novel andimproved sensor construction for use with the rear axle assembly of avehicle in which the sensing rings or poles of the sensor are mounted tothe axle shaft and axle housing in a manner providing substantially noradial and/or axial relative movement whereby a minimum air gap can bemaintained.

Other objects, features, and advantages of the present invention willbecome apparent from the subsequent description and the appended claims,taken in conjunction with the accompanying drawings, in which FIG. 1 isan elevational view with some parts shown in section and others brokenaway of a sensor assembly embodying features of the present invention;

FIG. 2 is a sectional view to reduced scale of the sensor assembly ofFIG. 1 taken generally along the lines 2-2;

FIG. 3 is a fragmentary view with some parts shown in section of amodified form of sensor assembly;

FIG. 4 is a fragmentary view with some parts shown in section of adifferent, modified form of sensor assembly; and

FIG. 5 is a sectional view taken generally along the lines 5- 5 in FIG.4.

Looking now to the FIGS. 1 and 2 of the drawing, the sensor assembly isgenerally indicated by the numeral and is shown in assembly relationshipwith a rear axle assembly 12 which rear axle assembly includes an axleshaft 14 which terminates at its outer end in a flange 16 to which awheel assembly (not shown) can be mounted. The axle shaft 14 isrotatably mounted within an axle housing assembly I8 to which at least aportion of the sensor assembly 10 is mounted.

The sensor has a stator or fixed pole member which is secured to theaxlehousing 18 through a radially extending flange 22. The stator 20 hasan axially extending annular portion 24 terminating in a plurality ofgenerally uniformly circumferentially disposed, radially extending teeth26. The axially extending portion 24 along with an annular ring 28defines an annular cavity 30 in which are located a permanent magnet 32and a coil assembly 34. The permanent magnet 32 is preferably of anannular ring construction having a polarity as indicated in FIG. I, Thecoil assembly 34 also extends annularly within the opening 30 andincludes an electrical coil 36 which is wound in a plastic bobbin 38.The bobbin 38 can be constructed of a material having good bearingcharacteristics such as Teflon for a purpose to be described. Theforward face 40 of the bobbin 38 extends beyond the axial extremity ofthe teeth 26 and also beyond the axial outer extremity of the ring 28for a purpose to be presently seen. The bobbin 38 is pro- I vided withan annular axially extending ring portion 42 which is piloted within anannular groove 44 located in an annature or rotor member 46. The rotoror pole member 46 is generally of a flat washer shape and has aplurality of uniformly circumferentially disposed radially extendingteeth 48 which =ar located in axial confrontation with the teeth 26. Theteeth 48 are radially longer than the teeth 26 for purposes to bedescribed. The armature 46 has a central circular opening 50 which isprovided with a plurality of radially outwardly extending slots 52. Thearmature 46 is made of a magnetic material and is held in bearingengagement against the outer face 40 of the bobbin 38 by the magneticattraction from the i field caused by the permanent magnet 32; theprojection 42 and groove 44 properly locate the teeth 48 of the armature46 relative to the teeth 26 of the stator 20. With the assembly as shownand described thus far a first airgap 54 is defined between the teeth 26and 48 and second airgap 56 is defined between the armature 46 and thering 28. The armature 46 is rotated by a drive ring 58 which is securedto the axle shaft 14 as by a press fit and hence will rotate therewith.The drive ring 58 has a plurality of radially outwardly extending tabs60 which are located with a clearance relationship all around, withinthe grooves 52 in armature 46; thus rotation of the shaft 14 will causerotation of armature 46 via the drive ring 58 resulting in an inducedpotential in coil 36 of a frequency indicative of the rotational speedof axle shaft 14. Note that since the material of the bobbin 38 has goodbearing characteristics the bearing surface 40 will provide only slightfrictional engagement with armature 46.

In the event of radial deflection of the axle shaft 14 relative to theaxle housing 18, the relative position between the armature 46 and thestator 20 will be unchanged since the tab 60 will be free to moveradially within slot 52 without disturbing the position of the armature46. Also, with this connection between the drive member 58 and armature46 relative axial movement between the axle shaft 14 and the axlehousing 18 can occur without relative motion occurring between thearmature 46 and the stator 20. Thus with the construction shown,relative axial and radial movement between the axle shaft 14 and theaxle housing 18 can occur without change in the air gaps 54 and 56;since these airgaps will be maintained at a constant width, they can beprovided to be of a minimum whereby the reluctance will be a minimumresulting in an efficient sensor. It can be seen from the constructionshown, some, slight radial movement can occur between the armature 46and the stator 20. However, the teeth 48 on armature 46 are longer thanthe teeth 26 and hence even with movement of the armature to its extremepositions there will be no change in the effective airgap between theteeth 36 and 48.

A slightly modified form is shown in FIG. 3 in which the interconnectionof projection 42 and groove 44 and the sliding bearing with the surface40 has been eliminated and an annular bearing assembly 70 has beensubstituted therefor. In FIG. 3 of the drawing, parts similar tocorresponding parts in the embodiment of FIGS. 1 and 2 are given thesame numeral designations with the addition of the letter a." In FIGS. 4and 5 a still different form is shown in which the drive ring 58 hasbeen eliminated and a flexible, resilient connection has been providedbetween the armature and the stator. In the embodiment of FIGS. 4 and 5components similar to like'components in FIG. 1 have been given similarnumeral designations with the addition of the letter b." Thus thearmature 46b is provided with a plurality of axially extending fingerportions 72. Drive ring 80 is made of a flexible material having aplurality of radially inwardly extending fingers 82 and 84 at itsradially inner surface which will grip the axle shaft 141: such that therotation of the axle shaft 14b will result in rotation of the flexibledrive ring 80. The drive member 80 also has a plurality of radiallyoutwardly extending fingers 86 at its outer periphery. in assembly, theaxial projections 72 will engage one of the fingers 86 depressing itradially inwardly as shown whereby the driving action will be providedby two circumferentially, ad-' jacent fingers; since the engagementbetween the drive member 80 and the armature 46b is by way of fingers 86any relative axial and radial movement will be accommodated by flexingof the engaging ones of the fingers 84 thereby again maintaining thewidths of airgap 54b and 56b constant. Note that radially inner fingers82 are longer than fingers 84; this provides better gripping and anaxially wider support base than if the fingers were of uniform length.Note also that assembly for driving engagement of armature 46b with thedrive ring 80 is simplified since no particular circumferentialalignment need be maintained (as with the tabs 60 and grooves 52) andany group of outer fingers 86 lining up with finger portions 72 willsuffice.

While it will be apparent that the preferred embodiments of theinvention disclosed are well calculated to fulfill the objects abovestated, it will be appreciated that the invention is susceptible tomodification, variation and change without departing from the properscope of fair meaning of the invention.

What is claimed is:

1. An electrical rotational speed sensor for providing an electricalsignal indicative of the rotational speed between a pair of members withone of the members supported for rotation relative to the other, thesensor comprising: a rotor connected to the one of the members forrotation therewith, a stator connected to the other of the membersproximate to said rotor, a magnetic path having a preselected airgapbetween confronting surfaces on said rotor and said stator, and mountingmeans mounting said rotor and said stator in predetermined positionsrelative to each other and maintaining said airgap substantiallyconstant through relative movement between the members in the axial andradial directions, said mounting means including drive means supportedon the one of the members for rotation therewith and coupling means forrotatably coupling said drive means and said rotor for rotation by theone of the members, said coupling means comprising a radially extendingtab located in a radially extending slot with a clearance therebetweenin the axial and radial directions for freely accepting relativemovement between the members in the axial and radial directions with theposition relationship between said rotor and stator being heldsubstantially constant in the direction of said airgap whereby forcesgenerated by said relative movement between said members is nottransmitted to said mounting means.

2. The sensor of claim 1 with said mounting means magnetically holdingsaid rotor and stator.

3. The sensor of claim 1 with both said rotor and said stator beingsupported on a first of the members.

4. The sensor of claim 1 with said rotor being generally in the shape ofa washer and having a fiat bearing surface, said stator having a flatsurface of bearing material and with said mounting means magneticallyholding said rotor and stator with said bearing surface engaging saidsurface of bearing material.

5. The sensor of claim 1 with an antifriction bearing member locatedbetween said rotor and said stator and with said mounting meansmagnetically holding said rotor and said stator together through saidantifriction member, said antifriction member extending annularly aboutthe axis of the one member and radially guiding and locating said rotorand said stator relative to each other.

6. The sensor of claim 1 with said confronting surfaces including afirst set of circularly disposed teeth and a second set of circularlydisposed teeth facing said first set with the teeth of one of said setsbeing longer than the teeth of the other of said sets whereby theeffective airgap will remain substantially the same through slightrelative movement between said rotor and said stator in a directionalong the length of the teeth.

7. An electrical rotational speed sensor for providing an electricalsignal indicative of the rotational speed between a pair of members withone of the members supported for rotation relative to the other, thesensor comprising: a rotor connected to the one of the members forrotation therewith being generally in the shape of a washer and having aflat bearing surface, a stator connected to the other of the membersproximate to said rotor having a flat surface of bearing material, amagnetic path having a preselected airgap between confronting surfaceson said rotor and said stator, and mounting means mounting said rotorand said stator in predetermined positions relative to each other andmaintaining said airgap substantially constant through relative movementbetween the members in one of axial and radial directions, with saidmounting means magnetically holding said rotor and stator with saidbearing surface engaging said surface of bearing material, guide andlocating means for radially guiding and locating said stator and rotorand comprising an annular groove on one of said bearing surface and saidsurface of bearing material and a circularly distributed projection onthe other of said bearing surface and said surface of bearing materiallocated in said annular groove, said mounting means including drivemeans connected with the one member and said rotor providing a clearancetherebetween in said one of axial and radial directions for freelyaccepting relative movement between the members in said one of axial andradial directions with the position relationship between said rotor andstator being held substantially constant in the direction of said airgapwhereby forces generated by said relative movement between said membersis not transmitted to said mounting means.

8. An electrical rotational speed sensor for providing an electricalsignal indicative of the rotational speed between a pair of members withone of the members supported for rotation relative to the other, thesensor comprising: a rotor connected to the one of the members forrotation therewith, a stator connected to the other of the membersproximate to said rotor, a magnetic path having a preselected airgapbetween confronting surfaces on said rotor and said stator, and mountingmeans mounting said rotor and said stator in predetermined positionsrelative to each other, said mounting means maintaining said airgapsubstantially constant through movement of the members both axially andradially, said mounting means including a drive ring supported on theone of the members for rotation therewith and coupling means forrotatably coupling said drive ring and said rotor for rotation of saidrotor by the one of the members, said coupling means comprising aradially extending tab located in a radially extending slot, said slotdefined by a plurality of generally radially extending, resilientfingers with one of said fingers being bent axially and with said tabgenerally axially engaging said one of said fingers and being locatedbetween two of said fingers on opposite sides of said one of saidfingers.

9. The sensor of claim 8 with said drive ring including said fingerswhich extend radially outwardly and further including a second pluralityof radially inwardly extending fingers for gripping the one of themembers.

10. The sensor of claim 9 with said confronting surfaces extendingradially with teeth on at least one of said surfaces.

11. An electrical rotational speed sensor for providing an electricalsignal indicative of the rotational speed between a pair of members withone of the members supported for rotation relative to the other, thesensor comprising: a rotor connected tothe, one of the members forrotation therewith, a stator connected to the other of the membersproximate to said rotor, a magnetic path having a preselected airgapbetween confronting surfaces on said rotor and said stator, and mountingmeans mounting said rotor and said stator in predeterslot defined by aplurality of generally radially extending, resilient fingers with one ofsaid fingers being bent axially and with said tab generally axiallyengaging said one of said fingers and being located between two of saidfingers on opposite sides of said one of said fingers.

1. An electrical rotational speed sensor for providing an electricalsignal indicative of the rotational speed between a pair of members withone of the members supported for rotation relative to the other, thesensor comprising: a rotor connected to the one of the members forrotation therewith, a stator connected to the other of tHe membersproximate to said rotor, a magnetic path having a preselected airgapbetween confronting surfaces on said rotor and said stator, and mountingmeans mounting said rotor and said stator in predetermined positionsrelative to each other and maintaining said airgap substantiallyconstant through relative movement between the members in the axial andradial directions, said mounting means including drive means supportedon the one of the members for rotation therewith and coupling means forrotatably coupling said drive means and said rotor for rotation by theone of the members, said coupling means comprising a radially extendingtab located in a radially extending slot with a clearance therebetweenin the axial and radial directions for freely accepting relativemovement between the members in the axial and radial directions with theposition relationship between said rotor and stator being heldsubstantially constant in the direction of said airgap whereby forcesgenerated by said relative movement between said members is nottransmitted to said mounting means.
 2. The sensor of claim 1 with saidmounting means magnetically holding said rotor and stator.
 3. The sensorof claim 1 with both said rotor and said stator being supported on afirst of the members.
 4. The sensor of claim 1 with said rotor beinggenerally in the shape of a washer and having a flat bearing surface,said stator having a flat surface of bearing material and with saidmounting means magnetically holding said rotor and stator with saidbearing surface engaging said surface of bearing material.
 5. The sensorof claim 1 with an antifriction bearing member located between saidrotor and said stator and with said mounting means magnetically holdingsaid rotor and said stator together through said antifriction member,said antifriction member extending annularly about the axis of the onemember and radially guiding and locating said rotor and said statorrelative to each other.
 6. The sensor of claim 1 with said confrontingsurfaces including a first set of circularly disposed teeth and a secondset of circularly disposed teeth facing said first set with the teeth ofone of said sets being longer than the teeth of the other of said setswhereby the effective airgap will remain substantially the same throughslight relative movement between said rotor and said stator in adirection along the length of the teeth.
 7. An electrical rotationalspeed sensor for providing an electrical signal indicative of therotational speed between a pair of members with one of the memberssupported for rotation relative to the other, the sensor comprising: arotor connected to the one of the members for rotation therewith beinggenerally in the shape of a washer and having a flat bearing surface, astator connected to the other of the members proximate to said rotorhaving a flat surface of bearing material, a magnetic path having apreselected airgap between confronting surfaces on said rotor and saidstator, and mounting means mounting said rotor and said stator inpredetermined positions relative to each other and maintaining saidairgap substantially constant through relative movement between themembers in one of axial and radial directions, with said mounting meansmagnetically holding said rotor and stator with said bearing surfaceengaging said surface of bearing material, guide and locating means forradially guiding and locating said stator and rotor and comprising anannular groove on one of said bearing surface and said surface ofbearing material and a circularly distributed projection on the other ofsaid bearing surface and said surface of bearing material located insaid annular groove, said mounting means including drive means connectedwith the one member and said rotor providing a clearance therebetween insaid one of axial and radial directions for freely accepting relativemovement between the members in said one of axial and radial directionswith the position reLationship between said rotor and stator being heldsubstantially constant in the direction of said airgap whereby forcesgenerated by said relative movement between said members is nottransmitted to said mounting means. located between two of said fingerson opposite sides of said one of said fingers.
 9. The sensor of claim 8with said drive ring including said fingers which extend radiallyoutwardly and further including a second plurality of radially inwardlyextending fingers for gripping the one of the members.
 10. The sensor ofclaim 9 with said confronting surfaces extending radially with teeth onat least one of said surfaces.
 11. An electrical rotational speed sensorfor providing an electrical signal indicative of the rotational speedbetween a pair of members with one of the members supported for rotationrelative to the other, the sensor comprising: a rotor connected to theone of the members for rotation therewith, a stator connected to theother of the members proximate to said rotor, a magnetic path having apreselected airgap between confronting surfaces on said rotor and saidstator, and mounting means mounting said rotor and said stator inpredetermined positions relative to each other, said mounting meansmaintaining said airgap substantially constant through movement of themembers both axially and radially, said mounting means includingcoupling means for rotatably coupling the one of the members and saidrotor for rotation of said rotor by the one of the members, saidcoupling means comprising a radially extending tab located in a radiallyextending slot, said slot defined by a plurality of generally radiallyextending, resilient fingers with one of said fingers being bent axiallyand with said tab generally axially engaging said one of said fingersand being located between two of said fingers on opposite sides of saidone of said fingers.